private static IAsyncPolicy GetPolicy(ILogger logger)
{
if (circuitBreakerPolicy == null)
{
circuitBreakerPolicy = Policy.Handle <Exception>().CircuitBreakerAsync(_errorCountForCircuitbreak, TimeSpan.FromMilliseconds(_circuitBreakDuration),
(ex, breakDelay) =>
{
logger.Log(LogSeverity.Error, (ex.InnerException != null) ? ex.InnerException.Message : ex.Message + "\r\n GetTrendingStocks Circuit broken");
},
() => { });
}
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromSeconds(_timeoutSeconds), TimeoutStrategy.Pessimistic);
var retryPolicy = Policy.Handle <Exception>((ex) =>
{
logger.Log(LogSeverity.Error, (ex.InnerException != null) ? ex.InnerException.Message : ex.Message + "\r\n GetTrendingStocks retry FAILURE");
return(!(ex is Polly.CircuitBreaker.BrokenCircuitException));
}).WaitAndRetryAsync(_retryCount, x => TimeSpan.FromMilliseconds(_sleepTimeAfterFail));
var pollyWrap = Policy.WrapAsync(circuitBreakerPolicy, timeoutPolicy, retryPolicy);
return(pollyWrap);
}
static void Main(string[] args)
{
var builder = new HostBuilder()
.ConfigureServices((hostContext, services) =>
{
// v1 services.AddHttpClient();
services.AddTransient <IMyService, MyService1>();
// v2 - named HttpClients
services.AddHttpClient("GitHub", client =>
{
// works
client.BaseAddress = new Uri("https://github.com/");
// doesn't (no header for API key)
// client.BaseAddress = new Uri("https://api.github.com/");
client.DefaultRequestHeaders.Add("Accept", "text/html"); // returned from HTML pages
// client.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json"); // not returned from HTML pages
});
// v3 retry against flaky service
services.AddHttpClient("flakyService", client =>
{
client.BaseAddress = new Uri("http://localhost:5000");
client.DefaultRequestHeaders.Add("Accept", "application/json"); // not returned from HTML pages
})
.AddTransientHttpErrorPolicy(builder => builder.WaitAndRetryAsync(new[] // v3 add HttpErrorPolicy for retry on 5XX and 408 errors
{
TimeSpan.FromSeconds(1),
TimeSpan.FromSeconds(5),
TimeSpan.FromSeconds(10)
}));
services.AddHttpClient("flakyServiceCB", client =>
{
client.BaseAddress = new Uri("http://localhost:5000");
client.DefaultRequestHeaders.Add("Accept", "application/json"); // not returned from HTML pages
});
}).UseConsoleLifetime();
var host = builder.Build();
using (var serviceScope = host.Services.CreateScope())
{
var services = serviceScope.ServiceProvider;
DateTime now = DateTime.Now, done;
try
{
// v1 (hardcoded)
MyService1 myService = (MyService1)services.GetRequiredService <IMyService>();
myService.URL = "http://www.microsoft.com";
Console.WriteLine(myService.GetPage().Result.Substring(0, 500));
// v2 (GitHub)
IHttpClientFactory _httpClientFactory = services.GetService <IHttpClientFactory>();
var client = _httpClientFactory.CreateClient("GitHub"); // pull the registered client out of factory
Console.WriteLine(client.GetStringAsync("/bwloomis").Result.Substring(0, 500));
// v3 - retry against flaky service
client = _httpClientFactory.CreateClient("flakyService"); // pull the registered client out of factory
Console.WriteLine(client.GetStringAsync("/weatherforecast?hitCount=2").Result);
Console.WriteLine("now trying one that won't work");
//now = DateTime.Now;
//Console.WriteLine(client.GetStringAsync("/weatherforecast?hitCount=3").Result);
//done = DateTime.Now;
//TimeSpan elapsed = done - now;
//Console.WriteLine($"took {elapsed.TotalMilliseconds} ms");
// v4 circuit breaker against flaky service (retry twice)
client = _httpClientFactory.CreateClient("flakyServiceCB"); // pull the registered client out of factory
Polly.CircuitBreaker.AsyncCircuitBreakerPolicy cbPolicy = Policy
.Handle <Exception /* HttpRequestException */>()
.CircuitBreakerAsync(
exceptionsAllowedBeforeBreaking: 1,
durationOfBreak: TimeSpan.FromMinutes(10), // if not a while, the breaker will reset before failures occur
(ex, t) =>
{
Console.WriteLine("***************** Circuit broken ***************************");
},
() =>
{
Console.WriteLine("Circuit reset");
});
Task <string> innerResponse;
// first try, succeeds
for (int i = 1; i <= 4; i++)
{
try
{
// first try passes in a 6 (succeeds), second try trips the breaker (with a 7), then others revert back to 6
int param = (i == 2) ? 7 : 6;
if (i == 4)
{
cbPolicy.Reset();
}
// if you do not check CB status, and it is open, then this will not be executed
var response = cbPolicy.ExecuteAsync <string>(async() =>
{
innerResponse = client.GetStringAsync($"/weatherforecast?hitCount={param}");
if (innerResponse != null)
{
Console.WriteLine($"innerResponse was: {innerResponse.Result}");
}
return((innerResponse != null) ? innerResponse.Result : null);
});
Console.WriteLine($"Circuit breaker is {cbPolicy.CircuitState.ToString()}");
Console.WriteLine();
}
catch (HttpRequestException hre) // typically do these through handlers on the policy, not through try/catch
{
// if you are securing an HTTP resource, you'll get a 503 error from time to time on our flaky service
Console.WriteLine($"An HTTP request exception occurred: {hre} {hre.InnerException}");
}
catch (Exception ex)
{
// this would be the other type of error, aggregate exception
Console.WriteLine($"An exception occurred: {ex} {ex.InnerException}");
}
}
// extra credit - add timeouts to calls...
}
catch (Exception ex)
{
done = DateTime.Now;
TimeSpan elapsed = done - now;
Console.WriteLine($"An error occurred: {ex} {ex.InnerException}");
Console.WriteLine($"took {elapsed.TotalMilliseconds} ms");
}
}
Console.ReadLine();
// host.RunAsync();
}
